Integrated circuit (IC) substrate manufacturing technology aims to reduce substrate size and cost and to increase functionality. A recent advance uses laser direct ablation (LDA) and special plating processes to form electrical signal traces or paths inside a dielectric layer, as opposed to forming signal traces on the surface of the dielectric layer using conventional lithography technology. The embedded trace approach reduces overall layer counts, improves cost and yield, and improves electrical performance by reducing signal length and optimizing trace routing. The embedded trace approach may be achieved by forming signal traces having widths that are 10 μm or less in conjunction with padless microvia design. Known methods for dielectric removal, however, lack productive and cost effective manufacturing techniques suitable for high-volume production.
Ultraviolet (UV) excimer and yttrium aluminum garnet (YAG) laser sources have been discussed for LDA. UV YAG systems can be operated in both vector and raster scanning methods. UV YAG architectures generally do not require an imaging mask. Thus, UV YAG systems offer flexibility and rapid adaption of design change. Excimer laser ablation, on the other hand, uses a mask projection technique to remove materials in a large area. Thus, excimer laser ablation can provide high throughput when a pattern includes many lands, ground planes, or other larger features. The throughput when using an excimer laser is independent from pattern density inside the mask area. However, increasing pattern density may significantly impact throughput in the case of direct writing methods using a UV YAG laser. Excimer ablation exhibits better resolution and depth control, as compared to those when using a UV YAG laser, because of uniform and incremental dielectric removal over the mask area. The power rating of a UV YAG laser may be from about 3 Watts to about 40 Watts, and the power rating of an excimer laser may be up to about 300 Watts. UV YAG lasers generally operate at a pulse repetition rate from about 50 kHz to about 250 kHz, while the pulse repetition rate of an excimer laser is generally a few hundreds of Hertz. UV YAG and Excimer laser systems both provide processing for a broad choice of dielectric materials due to the higher ablation in UV wavelengths (e.g., about 355 nm is typical for UV YAG lasers, and about 248 nm and about 308 nm are typical for excimer lasers).